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'Interleaved 2 of 5' is a continuous two-width barcode symbology encoding digits. It is used commercially on 135 film and on cartons of products, while the products inside are labeled with UPC or EAN.
I2/5 encodes pairs of digits; the first digit is encoded in the bars, while the second digit is encoded in the spaces interleaved with them. The digits are encoded as follows:

0 NNWWN

1 WNNNW

2 NWNNW

3 WWNNN

4 NNWNW

5 WNWNN

6 NWWNN

7 NNNWW

8 WNNWN

9 NWNWN

Before the actual pairs there is a start code consisting of NNNN, and after all symbols there is the stop code consisting of WNN.
As only an even number of digits can be encoded, a 0 is added as first digit. Sometimes an odd number of digits is encoded by putting five narrow spaces in the last pair.
A checksum can be added as last digit, which is calculated in the same way as UPC checksums.
There are very specific constraints on the height and width of the bars and the width of the "quiet areas", the blank areas before the start and after the stop symbol. See http://www.barcode-1.net/pub/russadam/i25code.html and http://www.spatula.net/proc/barcode/i25.src for more information.
On 135 film (35 mm) canisters it is used to identify the manufacturer, the film type, number of exposures and proprietary information in 6 digits.
The barcode is located between the electrically read silver and black DX Camera Auto-Sensing Code and the film can exit lip.
The barcode is optically scanned by many film-processing machines when the cartridge is inserted for developing. (see Kodak patent 5761558)
Identcode and Leitcode are variants of interleaved 2 of 5 with check digits used by Deutsche Post.

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See also

See also

★ ITF-14

★ Two-out-of-five code

★ Linear barcodes